6.PROPERTIES OF CERAMICS MATERI BELAJAR.pptx

Ceramic

1. PROPERTIES OF CERAMICS Sitti Ahmiatri Saptari

2. Properties of Ceramic Materials • High hardness, electrical and thermal insulating, chemical stability, and high melting temperatures • Brittle, virtually no ductility - can cause problems in both processing and performance of ceramic products • Some ceramics are translucent, window glass (based on silica) being the clearest example

3. Properties of Ceramics Density - in general, ceramics are lighter than metals and heavier than polymers Melting temperatures - higher than for most metals, some ceramics decompose rather than melt Electrical and thermal conductivities - lower than for metals; but the range of values is greater, so some ceramics are insulators while others are conductors Thermal expansion - somewhat less than for metals, but effects are more damaging because of brittleness

4. Flexural strenght

5. EXAMPLE PROBLEM A three-point bending test is performed on a spinel (MgAl 2 O 4 ) specimen having a rectangular cross section of height d 3.8 mm and width b 9 mm; the distance between support points is 25 mm. Compute the flexural strength if the load at fracture is 350 N .

6. MAGNETIC CERAMICS Materials may be classified by their response to externally applied magnetic fields as • diamagnetic, • paramagnetic, or • ferromagnetic.

7. Diamagnetic Diamagnetic materials have a weak, negative susceptibility to magnetic fields. Ex : SiO2 (quartz), CaCO3 (calcite)

8. Paramagnetic Paramagnetic materials have a small, positive susceptibility to magnetic fields. These materials are slightly attracted by a magnetic field and the material does not retain the magnetic properties when the external field is removed. Paramagnetic properties are due to the presence of some unpaired electrons, and from the realignment of the electron paths caused by the external magnetic field.

9. Ferromagnetic Ferromagnetic materials have a large, positive susceptibility to an external magnetic field. They exhibit a strong attraction to magnetic fields and are able to retain their magnetic properties after the external field has been removed.

10. Soft & hard magnetic Soft magnetic, do have the ability to store magnetic energy that has been converted from electrical energy; but it is normally short-term in nature because of the ease to demagnetize. • Hard magnetic materials (PMs) are comparatively difficult to demagnetize, so the energy storage time frame should be quite long.

11. Ferrites Among the magnetic ceramics, ferrites are the prodominant class. Ferrites using Fe 2 O 3 as the major raw material. Ferrites crystallize in a large variety of structures: • Spinel, • Garnet, and • Magnetoplumbite. Spinel: 1 Fe 2 O 3 : 1 MeO, (MeO=transition metal oxide). Garnet: 5 Fe 2 O 3 : 3 Me 2 O 3 (Me 2 O 3 =rare earth metal oxide) Magnetoplumbite: 6 Fe 2 O 3 : 1 MeO (MeO=divalent metal oxide from group II, BaO, CaO, SrO).

12. Magnetoresistance effect In magnetoresistive effect, the resistance of a material changes in the presence of magnetic field. Intrinsic magnetoresistance • SrRuO 3 • CrO 2 • La 0.7 (Ca 1-y Sr y ) 0.3 MnO 3 • Fe 3 O 4 • CaCu 3 Mn 4 O 12 (CCMO)